With an increase in consumption of fossil fuels, the problem of global warming, which is considered to be caused by the greenhouse effect caused by carbon dioxide, which is the combustion product of fossil fuels, has come to be serious. Meanwhile, the following methods have been studied for thermal power plants and the like that use a large amount of fossil fuels: a method of separating and recovering carbon dioxide contained in combustion exhaust gas by bringing the combustion exhaust gas into contact with an amine-based absorption liquid and a method of storing the recovered carbon dioxide without discharging the recovered carbon dioxide into the air.
As a specific system that separates and recovers carbon dioxide, there is known a system that includes an absorption column and a regeneration column. The absorption column allows carbon dioxide that is contained in an exhaust gas to be absorbed in an absorption liquid. The regeneration column discharges the carbon dioxide by heating the absorption liquid (rich liquid), which contains the absorbed carbon dioxide and is supplied from the absorption column, by a reboiler, and recycles the absorption liquid used once into an absorption liquid (lean liquid) that does not contain the carbon dioxide through the discharge of the carbon dioxide from the used absorption liquid. Then the regenerated absorption liquid is circulated in the absorption column.
There has been proposed methods using steam as a heat source of the reboiler for this system: a method in which the steam extracted from a low-pressure turbine or the steam exhausted from a second intermediate-pressure turbine are used as the heat source, a method in which the steam exhausted or extracted from a turbine for driving a compressor to compress or cool the carbon dioxide is used as the heat source, and a method in which the steam extracted from an intermediate stage of a turbine is used as the heat source, and the like.
Further, there has been proposed a system that supplies steam, which is extracted from an intermediate stage of an existing turbine, to the added turbine when a new turbine is added to an existing power generation plant in order to increase an output.
It is considered a case of a carbon dioxide separation recovery system is simultaneously installed together with a power generation system that includes a boiler, a turbine, a generator, and the like; and a case of a carbon dioxide separation recovery system is added to an existing power generation system.
When a carbon dioxide separation recovery system is added to an existing power generation system, it is very important from which portion of an existing power generation system a heat source is taken to the reboiler of a carbon dioxide separation recovery system. A new steam line, a new second intermediate-pressure turbine, or a new turbine for driving a compressor to compress or cool the carbon dioxide are required to be installed in all of the above-mentioned related arts, in order to supply a heat source to a reboiler. Modifications for these are not easy.
Further, when steam is extracted from an intermediate stage of an existing turbine and supplied to a reboiler, the pressure balance of an existing turbine is lost. For this reason, it is difficult to maintain the same performance of a turbine as that was obtained before a carbon dioxide separation recovery system is added.
Furthermore, in the operation of a general power generation system, it is important to maintain an electrical output corresponding to a power supply command. However, in the above-mentioned related arts, the amount of steam supplied to a turbine from a boiler for driving a generator is changed due to the change of the amount of steam supplied to a reboiler of a carbon dioxide separation recovery system, so that the electrical output has been changed. As described above, in the past, there have been problems in that and it was difficult to separate and recover carbon dioxide with maintaining the appropriate electrical output corresponding to the power supply command with preventing the deteriorating of the tubine performance.